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Illinois Institute 

of Technology 

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*|AT 292 

■Ford, Thomas Cecil 
Modern bituminous roads and 
I pavements 



MODERN BITUMINOUS ROADS AND PAVEMENTS 
A THESIS 

PRESENTED BY 
THOMAS CEC IL FORD 

TO THE 

PRESIDENT AND FACULTY 
OF 
ARMOUR INSTITUTE OF TECHNOLOGY 



FOR THE DEGREE OF CHEMICAL ENGINEER 



1913 



ILLINOIS INSTITUTE OF TECHNOLOGY 
PAULV GALVIN LIBRARY 
35 WEST 33RD STREET 
CHICAGO, IL 60616 







(oZS'.Q 



MODERN BITUMINOUS 
ROADS AND PAVEMENTS 



Perhaps no other subject, today, has such a genuine 
interest in the minds of the public as that of good roads. 
All over the United States as well as other nations, the 
people are awakening to the fact that good roads are essen- 
tial to the rapid growth and development of the country. 
The ease and comfort of travel on highways are only acquired 
by improvement of the roadways. 

The national government has a department devoted 
wholly to the advancement and aid in road building. Nearly 
every state in the union has a highway department which 
looks after the building and maintaining of its roads. Every 
city has a department which is devoted to the improvement 
and maintenance of its streets and pavements. Millions of 
dollars are spent annually and yet the demand for more and 
better roads is rapidly increasing. 

Up to the present time the United States Office of 
Public Roads has devoted its efforts to the aid of state and 
country work in demonstrative and advisory way but recently 
there was a bill introduced in Congress which provides for 
the building and maintaining of a system of National Highways 



to "be "built and maintained "by the national government. 
This system of roads would connect all the state capitols 
and cities of over 20,000 inhabitants. It would require 
18,000 miles of roads at a cost of about 270,000,000 
dollars. 

Numerous societies have "been organized for the advance- 
ment of the good road movement, among which are, "The 
Permanent International Road Congress", "The American 
Highway Association", "American Road Builders Association", 
"American Automobile Association", "American Association for 
the Standardization of Paving Specifications", "American 
Society for Municipal Improvements", and others. 

The highway problems have for several years been 
attacked along scientific lines until road building has 
now become a science and an art. 

Specifications for the same classes of roads and 
TDavements in different cities and states have varied 
so that an attempt has been made to standardize them and thus 
get better and more uniform results at a less expense. This 
work has been done largely by the American Association 
for the Standardization of Paving Specifications and the 
American Society for Municipal Improvement. 

There are many types of construction of roads and 



pavements which might "be of interest but only those in 
which bituminous materials are used will "be considered 
here. 

The first "bituminous pavements in this country were 
laid in Brooklyn in 1867. This pavement was a mixture 
of broken stone, gravel, ashes and tar. Soon after sim- 
ilar pavements were laid in Washington, D.C. and other 
towns with more or less success. In 1878 Trinidad asphalt 
was used in paving Delaware Ave., Buffalo, N.Y. ; Newark, 
N.J. ; New York City and Washington, D.C. soon followed in 
the use of asphalt and from then until now its use has in- 
creased with surprising rapidity until there are now many 
million square yards of pavement in the U.S. laid with 
various kinds of asphalt, which have been produced to meet 
the great demand for it. 

Bituminous pavements may be classified as follows :- 

Sheet Asphalt 
Asphalt Block 
Asphaltic Concrete 
Asphalt Macadam 
Bituminous Surfaces 



A Sheet Asphalt pavement is one consisting of a mixture 
of sand, dust and asphalt cement in varying proportions, 
spread on a firm foundation and rolled to an even surface. 
Usually the pavement is laid in two courses; the first or 
hinder course, consisting of a mixture of "broken stone, 
with sometimes a little sand and asphalt cement. The thick- 
ness of the hinder course varies from an inch to an inch and 
a half* The surface or top course as described above varies 
from one and a half to two inches in thickness. 

The foundation for all pavements should be firm and 
even. The surface and under-drainage should be ample to 
take care of all surplus water and thus insure the pavement 
against its damaging effects, which are principally the weak- 
ening of the foundation and the disintigration of the bitum- 
inous mixture from the emulsifying effect on the asphalt 
cement. This latter effect is much more noticeable with 
some asphalts, such as Trinidad, than others. For sheet 
asphalt nothing but a good concrete foundation should be 
used. Any sinking or giving of the foundation will cause 
defects in the surface which are difficult to repair. 

Every material entering into a paving mixture should 
be tested before its use* The sand, stone and dust com- 
prising the mineral aggregate are tested for grading which 



consists in separating into different sizes by means of 
screens. The grading of the "binder aggregate is not so 
important as that of the topping. The following are the 
limits given "by the American Society for Municipal Im- 
provements :- 

Passing 10 mesh 10 - 35 % 

■ 2 " 10-35% 
M 1 " 20 - 60 £ 

■ l^L n 15-55^ 

The quality and grading of the sand used in a top mix- 
ture is more important because it constitutes approximately 
78 % of the mix. The following standard gradings are 
given "by Richardson: - 

Heavy Traffic Light Traffic 

0.0) 0.0) 
17.0) 2>A% 10.0) 20.0% 
17.0) 10.0) 

30.0) 30.0) 

13.0) 43*; 15. ) 45.0% 

10.0) 15 ) 
8.0) 23^ 10 j 35,0f o 
5.0) 10 ) 

In practical construction it is seldom that a sand or 

combination of sands can be obtained, at a reasonable cost, 

that will conform strictly to the above gradings but it is 



Passing 


200 


mesh 


H 


100 


ii 


ii 


80 


•i 


w 


50 


ii 


N 


40 


ii 


« 


30 


ii 


H 


20 


it 


N 


10 


H 



well to keep as near these limits as possible. 



Richardson gives the following analyses as standards 



for top mixtures:- 



Bitumen 






Passing 


200 


mesh 


H 


100 


■ 


ii 


80 


ii 


n 


50 


ii 


H 


40 


H 


n 


30 


•i 


ii 


20 


•i 


ii 


10 


ii 



Heavy Traffic 
10.5 7o 

13.0ft 

13.0f o 
13.0% 

23 . 5f 

n.OTo 

8.0f 

5.0< 

3.0* 



Light Traffic 
10.0% 

lO.Ofa 

9.0fo 
9.0f fl 

26. (W 

12.0% 

10.0<£ 
8.0# 
6.0% 



To give an idea of how nearly these standards may be 
followed, typical analyses of mixes used by the writer, are 
given below: 



Bitumen 200 100 80 50 40 30 20 10 Total 



Guthrie, Okla. 10.0 9.8 

Sapulpa, " 10.2 11.2 

St Louis, Mo. 10.3 11.4 

Titusville,Pa.lO.O 8.0 

Montreal, Can. 10,0 9.0 

Victoria, B.C. 10. 5 6.7 

Spokane, Wash. 11,0 10.0 

Wheeling, W.Va. 9.0 5.0 

Standard 10.0 10.0 



11.1 

15.6 
6.0 17.0 35.0 
7.0 17.0 34.0 



9.6 30.9 9.6 9.0 

7.5 28.5 10.0 12.0 

5.3 6.0 

7.0 8.0 

9.3 11.5 30.2 10.6 10.2 

12.7 7.4 23.2 16,9 7.4 

18.0 10.0 19.0 7.0 10.0 

2.0 2.0 15.0 14.0 24.0 

9.0 9.0 26.0 12.0 10,0 



7.0 


3.0 


100 


3.0 


2.0 


iob 


5.0 


4.0 


100 


5.0 


4.0 


100 


7.2 


2.0 


100 


7.5 


7.7 


100 


8.0 


7.0 


100 


0.0 


19.0 


100 




6.0 


100 



With each of the above mixtures most results have been 
obtained. Some of the pavements have been four years with 
no repairs. The mixture at Wheeling, W. Va, is hardly to be 
recommended, and just how well it will wear is a question as 



it has been down less than a year but is now in excellent 
condition. 

The amount of asphalt cement used in a pavement mixture 
depends on the kind and quality of; first, the asphalt cement; 
second, the sand and third, the filler or dust. All other 
things being equal the specific gravity of the materials is the 
basis upon which the percentage of the ingredients of the mix- 
ture is determined. In other words the ingredients should be 
used according to a percentage by volume rather than by weight. 
Considering the same aggregate it will take less asphalt cement 
by weight to cover every particle with the same thickness of 
asphalt using one having a specific gravity of .980 than it 
will without having a specific gravity of 1.07. If the same 
asphalt cement be used with two different aggregates having 
the same grading and a different specific gravity, then the 
one having the greater specific gravity will require the 
lesser percentage of asphalt by weight because the surface per 
unit weight is less. The purity of the asphalt cement also effects 
the amount to be used. If an asphalt cement has a purity, i.e. 
bitumen soluble in carbon disulphide, of 99.5 °lo it will re- 
quire less than one having only 56.0 % bitumen. 



% 


Purity 


of 


Asphalt 


(1- 


99.5 


2- 


56.0 


Various (3- 


94.5 


Grades of (4- 


71.0 


Asphalt (5- 


99.5 


(6- 


99.5 



Cu. ft. 


Sq. Yds 


p. ton. 


2"Top 




Laid p.t 


32.5 


98 


16.7 


51 


28.3 


86 


20.9 


63 


30.3 


92 


30.5 


92 



These differences are shown clearly "by the following table :- 

No. lbs. Gravity c 
Bitumen per pure 

ton bitumen 

1990 .980 

1120 1.071 

1890 1.068 

1420 1,086 

1990 1.050 

1990 1.045 



The quality and grading of the sand are very important 
factors in determining the amount of asphalt cement to be used 
in a mix. If a sand is hard and smooth grained it will not 
carry as much asphalt as if it were softer and more porous, 
without producing a "sloppy" mixture, i.e. one in which the 
asphalt will flush to the top of a load after a little jarring. 
The river and lake sands are usually smoother and more rounded 
than the bank sands; due to the scrubbing and grinding action 
of the water. The bank sands seem to have a more porous sur- 
face probably formed by a deposit of hydrosilicate about the 
surface of the grains. As a rule the finer the grading of the 
aggregate the more asphalt it will requir to produce a satis- 
factory mixture. In extreme cases these two factors may cause 
a variance of as much as 3 % in the asphalt used* 

V/hat has been said about gravity and grading of sand 
applies equally well to dust as it is used as a filler to de- 
crease the voids in the sand and to increase the toughness of 
the mixture. 



The most common fillers are limestone dust and Portland cement 
which have from 70%to 85 "Jo of material which will pass a 200 
mesh screen. In the state of Washington and the province of 
British Columbia there are large deposits of very fine sand, 
65 to 80 % of which will pass a 200 mesh screen. These sands 
have "been used very successfully as a filler in sheet asphalt. 

There are a number of different kinds of asphalt used in 
sheet asphalt work and much has been written concerning them, 
therefore no attempt will be made to give a description of the dif 
ferent crude materials but rather the sources, characteristics 
and qualities of the different asphalt cements which is the form 
in which the asphalt is used in the mixture. 

An asphalt cement, A. C, is prepared by refining and 
fluxing with a residuum oil, a crude native asphalt or semi- 
asphaltic oil until the residue has a penetration between 45 
and 100 when tested at 25° C. for 5 seconds with a No*2 needle 
weighted with 100. grame. 

Table no.l gives the analyses of different asphalt cements 
as prepared and used by the leading companies of the United States 
in 1912. Included in this table are the following asphalt 
cements: Pioneer. , Bermudez, Trinidad, Texaco, California, Cuban 
and Aztec. Pioneer is Utah Gilsonite, a crude native asphalt, 



10 



fluxed with a specially prepared flux. Bermudez is a natural 
asphalt, from a lake in Venezula, fluxed with a heavy residuum oiL 
Trinidad is also a native asphalt, from a lake deposit in the 
Island of Trinidad, fluxed with a residuum oil. Texaco is an 
oil asphalt prepared "by distilling a crude Texas oil until the 
residue has the proper consistency. California is another oil 
asphalt prepared the same as Texaco "but from crude California 
oil. Aztec has just been introduced on the market within the 
last two years and its value as a paving cement is questionable 
yet as it has had no service tests. It is prepared from a 
crude Mexican oil of which there is an abundant supply. 



TABLE NO. I 



11 



Material Pioneer Bermudez 

A.C. A.C. no. 2. 

Specific Gravity .9930 1.0760 

Melting Point 77 ft C. 61° C. 

FlashPoint (C.T.) 195° C. 

Ductility 0° C. 3 era. cm. 

■ 25° C. 6 cm. 40 cm. 

Penetration 0° C. 200 gr.lmin. 47 12 

" 25° C. 100 gr.5 sec. 78 50 

" 46° C. 50 gr.5 sec. 206 280 

Lose 17° C. 5 hrs. 1.2% 3.3^ 

Penetration Residue 25° C. 58 21 

Soluble in CS^ 99.77 94.15% 

Organic matter insoluble .12 1.80 f 

Ash .22 4.05 «£ 

Soluble in CC1 4 99.60 94. 25^ 

" "2 88 Beaurae Naptha 71.53 70.17°; 

Fixed Carbon 9.43 10. 21^ 



Trinidad 
A.C. 

1.2880 

62.5 c 

305* C, 

8 cm. 

36 cm. 

12 

50 

285 

2.3f a 

21 

64.94°7a 
5.33 % 
29.73% 
65.58% 
46.13<f. 
5.87ft 



Material 



Specific Gravity 
Melting Point 
Flash Point (C.T. 
Ductility 0° C. 
250 c. 



Texaco California 
A.C. A. C. . 



1.2880 
640 C. 
232° C. 
3 cm. 
21 cm. 



Penetration 0° C.200 gr.l min.25 
■ 25 c.100 gr.5 sec. 55 
" 4fio c. 50 gr.5 sec. 200 



Lose 170° C. 5 hrs. 

Penetration Residue 25° C 

Soluble in CS 

Organic Matter Insoluble 

Ash 

Soluble in CC1 4 

■ "2 88 Beaume Naptha74.66£ 

Fixed Carbon 9.84^ 



.25% 

38 

99.65% 
.10 f 
.25 £ 
99.70^ 



1.0453 
59° 

cm. 
100 cm 
13 
70 
320 
1.4% 

27 
99,58*0 
.22*; 
.20£ 
99.60^, 
76.00^ 
11.66& 



Cuban 
A.C. 

1.0933 

61° 
215° 

4 om. 
28 cm. 
23 
68 
242 

47 

89.38S 
'1.78* 

8.94% 
89. lift 
67.68^ 

9 . 10 f a 



Aztec 
A.C. 

1.0455 

67° 
265« 
OCin 
65fcm 
18 c 
54° 
290 

37 

99.60% 
.25?! 
.15f. 

88.75?. 
68.86% 
15.54f 



Pioneer is Utah Gisonite fluxed with a special oil. 
Berraudez is a solid native bitumen fluxed with a residuum oil. 
Trinidad is a solid native bitumen fluxed with a residuum oil. 
Texaco is an oil asphalt prepared from crude Texas oil. 
California is an oil asphalt prepared from crude California oil, 
Cuban is a solid native bitumen fluxed with a residuum oil. 
Aztec is an oil asphalt prepared from crude Mexican oil. 



12 



No attempt will be made to give a description of the methods 
used in making the above tests as a complete and detailed de- 
scription may "be found in Bulletin no. 38 of the U.S.O.P.R. 

The principal uses of the specific gravity test are its 
aid in identifying the asphalt and in determining the percentage 
to he used in a mixture as described above. It is sometimes used 
as a method of control in the preparation of bituminous materials 
It does not however indicate the value of a paving cement as 
has been the contention of some engineers. 

The melting point of an A.C. is a very important considera- 
tion in determining its suitability for use in a paving mixture. 
It will be noted from the table, No. 1, that the melting points 
are fairly uniform with the exception of Pioneer which is con- 
siderable higher. Upon carefull examination of numerous pave- 
ments laid with these various materials it was found that those 
with the lower melting point were much more affected by the 
summer heat, getting soft and marking badly under traff ic,while 
dunng the cold winter weather they became very hard and slippery. 
The material with the higher melting point did not show these 
effects nearly so much. Of course the susceptibility to temper- 
ature changes as shown by the different penetrations bring out 
these characteristics more clearly. It is not advisable to have 
too high a melting point though., for this makes the material 
much harder to handle and requires a higher temperature of the 



13 



mixture which, of course, adds to the cost. 

The penetration test is one of the most valuable in deciding 
upon the proper quality of the asphalt to "be used. This test is 
made at three different temperatures as follows: 

1. 0° C.No.2 needle weighted with 200 grams for 1 minute. 
2 25° C." ■ n ■ " 100 " ■ 5 seconds 

3.45 c." " ■ " " 50 " " 5 ■ 

The first test is used to determine the proper consistency 
at which the A.C. is to he used and is a means of control in its 
preparation. If any one refined asphalt he fluxed to a certain 
consistency then all the other chemical and physical properties 
will change proportionately so that the one test is all that is 
necessary to make after complete analysis has "been made at that 
consistency. The three tests corahined are used to determine 
the susceptibility to temperature changes, which has a great 
hearing upon the characteristics of the pavement. A pavement 
laid with an A.C. which has a high ratio between the penetration 
at tt C. and 45 a C. will become very soft and will mark badly 
during the hot summer months, and in the cold winter months it 
will become very hard and slippery as well as noisy, while one 
laid with an A.C. having a low ration betv/een the penetration 
at 0* C. and 45° C. will not get so soft and mark up so badly 
in the hot summer months nor will it get so hard, slippery or 
noisy in the winter months. These characteristics are very 



14 



marked in pavements laid with different materials. 

The ductility test is claimed by many chemists and engi- 
neers to "be a measure of the cohesiveness and cementitiousness 
of the asphalt and it is further claimed that a high ductility 
at 25° C. is essential to a good paving cement. Materials having 
a high ductility have a high susceptibility to temperature changes 
and become very hard and brittle when cold. From the above it 
will be noted that the materials having a high ductility at 25° C. 
have no ductility at 0° C, while the one having a low ductility 
at 25° C. has about half as much at 0° C. It is when the pave- 
ment is cold that it contracts and needs a ductile material, when 
it is hot it expands and does not need it. 

The loss at 170° C. for 5 hrs. and the penetration of the 
residue at 25° C. is determined to get by a quick method some 
idea as to what will be the effect of time on the cement after it 
is in the pavement. One having a high loss would naturally be 
affected more than one with a low loss all other things being equal. 
An exceptionally high loss accompained with a low flash point 
would indicate that too light an oil had been used for fluxing. 

The solubility in carbon disulphide gives the purity of the 
asphalt, which is the amount of bituminous binding material in it. 

88° Beaume paraffine naptha separates the bitumen into two 
classes, each composed of various hydrocarbons. Those hydro- 



15 



cartons insoluble in the naptha give body and consistency to the 
asphalt cement, and is probably a measure of the adhesiveness. In 
the materials of the above table there is very little difference 
in the percentage soluble in 88° Beaume paraffin naptha. 

When an asphalt has been overheated some of the hydro- 
carbons will be broken down into compounds containing a very 
large percentage of carbon known as carbenes. These compounds 
are insoluble in carbon tetrachloride but soluble in carbon di- 
sulphide so that their presence is determined by the difference 
in the solubility in the two solvents. It may happen in good 
asphalts which have not been over heated that they will be slight- 
ly more soluble in carbon tetrachloride than in carbon bisul- 
phide. A very small percentage of carbenes will render a 
material unfit for use in pavements. The presence of carbenes 
may also be detected by a microscopic examination. 

The fixed carbon is determined by an arbitrary method the 

same as is used in coal analysis, and gives some idea as to 

the proportion of the heavier hydrocarbons present. It is of 

most value in testing oil asphalts such as California and 

Mexican, for these often show a very high percentage of fixed 

carbon which indicates that the asphalt has been distilled too 

rapidly at a high temperature. 15% should be the maximum 
allowable fixed carbon content. 



Among the most important features of a successful bitu- 
minous pavement is the proper handling of materials both at 
the plant and on the street. There is no doubt but that a 
majority of the failures are due either to carelessness or 
ignorance in construction. After a proper mixture has been 
determined it is essential that it be kept uniform, and the 
temperature be kept within certain limits usually 275° F. , 
depending on the melting point of the A.C. and the distance 
to be hauled. The question is often raised as to why the 
maximum temperature is only 375° F. when the temperature 
used in refining is in some cases 600° F. It is found 
that when the bitumen is in a thin coat around the hot parti- 
cles of sand and stone that it is burned at a much lower 
temperature than when heated in bulk and only a small propor- 
tion exposed to the air, therefore the temperature of the 
mixture must be lower. 

The uniformity of the ingredients in a mixture can only 
be obtained by the most careful supervision. It is necessary 
to make tests of the grading of the nineral aggregates at 
least three or four times a day and tests for bitumen from 
representative "pot" samples should be made at least twice a 
day. 

The laying on the street consists of spreading, raking 
and rolling. When a load reaches the street it is dumped 



17 



from the wagon just far enough ahead of what has been laid 
so that the shovellers can spread it without having to carry- 
any ahead. After spreading.it should he well raked and 
"combed 1 ' until it is true to grade. The raking is very import- 
ant and only experienced men should he employed. The rolling 
is usually done with two rollers, a five ton and an eight ton. 
The first or surface rolling is done with the smaller roller 
just as quickly as the material is cold enough so that it will 
not blister under the roller. A water spray is used on the 
wheels of the roller to prevent the mixture picking up or 
sticking to the wheels. If the surface rolling is delayed 
until the mixture gets too cold it will "honeycomb" and the 
proper compression will not be obtained. In some cases the 
surface will chill so that no amount of rolling can thorough- 
ly compress it and the pavement will be porous and absorb 
water, which will be shown by the surface remaining damp for 
a long time after a rain. When this condition exits the 
water will freeze and the expansion will cause the pavement 
to disintegrate. In one case a pavement constructed with 

California where this condition existed, a heavy rain, f ol- 
lowed by freezing and thawing weather caused the asphalt 

which became hard and brittle to break loose from the ag- 
gregate and was washed into the gutter. The surface 
rolling should be followed by a thin coat of Portland 



18 



cement swept over the surface just ahead of the larger rol- 
ler which is run very slowly, giving the surface a straight 
and double diagonal roll until it is smooth, even and free from 
roller marks and will show no indentation from the roller. 

Sometimes the rolling will produce numerous surface 
crales extending from \ " to an 1" in depth. This may be 
caused by movement of the binder stone, slipping or creep- 
ing of the top on smooth concrete when no binder course is 
used or a burnt or dry mixture, i.e. one without sufficient 
A. C. in it. 

An asphalt block pavement is one composed of blocks 
about 2" x 4" x 8" made by compressing with about 240 tons 
pressure a mixture of-^ " stone chips, sand, dust and A.C. 
An A.C. with a very low penetration usually 15, is used 
in making these blocks, as well as a very low percentage of 
bitumen. The following is a typical analysis:- 



Bitumen 




7.5<7 


Passing 


200 mesh 


13.0 f 6 


n 


100 ■ 


3.0<% 


n 


80 " 


3.5«? 


H 


50 " 


8.0^. 


H 


40 " 


5.0% 


II 


30 " 


4.0 £ 


II 


20 " 


6.0% 


N 


10 " 


14. 0^ 


it 


8 " 


7.o*; 


N 


'/4- " 


22.0% 


II 


Va. ■ 


7.0ft 



The blocks are laid similar to brick on a concrete 



19 



foundation with about 1" cushion of a 1-3 sand cement mix 
fairly dry. 

Asphaltic concrete is a pavement composed of a mixture 
of crushed stone, sand, A.C. and in some cases dust. There 
are three distinct types of asphaltic concrete which will 
"be designated as Type A, E and C. 

Type A is what is known as Topeka mix. This name was 
given it "because it is the mix described in .the specifica- 
tions of Topeka, Kansas upon which the Warren Eros. Co. of 
Eoston tries to get an injunction against the City on the 
grounds of infringement of their patent no. 665725. The 
court ruled that this was not an infringement and Warren 
Eros, signed the decree of the court acknowledging it to "be 
correct. 

The specifications for this mix are as follows: 

Bitumen 7 - 11% 

Mineral Aggregate 

Passing 200 Mesh 5-11'% 

" 40 ■ 18 - 32%, 

n 10 " 25 55% 

" 4 " 8 - 22f 

" 2 " less than 10% 

Some pavements laid under this specification are given 
a flush or Squeegee coat of asphalt followed by a thin coat- 
ing of clean half inch crushed rock screenings or coarse 
torpedo sand. The purpose of the flush coat and screenings 



20 



is to fill the surface voids and seal it making it imper- 
vious to water. The screenings are worked into the flush 
coat "by traffic until it finally has an appearance simi- 
lar to sheet asphalt. 

The crushed rock used should he trap, "hard heads" , 
granite, hard limestone or any good durable stone. It is 
"better to have the stone free from dust as it is usually 
distributed very uniformly which makes it difficult to get 
a uniform grading of the aggregate, "besides this the dust 
is apt to form a crust about the particles of stone if it 
becomes wet and when dried it will not come off and when 
the asphalt is added it does not penetrate to the stone 
and thus the mixture will be apt to have loose stones 
which are liahle to cause ravelling, i.e., picking out of 
the stone under traffic. 

The A.C. used in this class of work is very similar 
to that used in sheet asphalt, in fact some companies use 
the same material. 

In this class of construction the low ductile asphalts 
such as "Pioneer" is particularly well adapted especially 
where a flush coat is used as it does not get "brittle and 
chip out under traffic in cold weather as the high ductile 
materials do. In order to overcome this ravelling some 
companies use a much higher percent of asphalt in the mix, 



21 



e.g., in N.Y. City last year one company used as high as 10.67o 
of Mexican asphalt. A sample from this work showed the fol- 
lowing analysis: 

Bitumen 3.0.6% 

Passing 200 M 7. Of. 

■ 80 15. Of. 

■ 40 19,0% 
" 20 20.4r 
" 10 10. Of. 
" -%- 13.0% 

)%. 5.0^ 

This pavement may be laid on concrete, macadam, old 
"brick or stone as a foundation. If it is laid on macadam 
great care must "be taken to see that there are no soft 
or spongy places in it, but if the macadam is good, equal 
if not better results may be obtained. 

What has been said regarding the construction of sheet 
asphalt pavements applies equally well to asphaltic concrete 
and as this subject was discussed in some detail, it will not 
be repeated here. 

This class of pavement has been very popular in the 
last two years, many thousand yards have been laid with ex- 
cellent results. It is particularly well adapted to heavy 
automobile traffic -with medium horse drawn traffic. In 
1T.Y. City last year over 100 miles were laid. A great deal 
of it having a very heavy horse drawn traffic with heavy 



22 



auto traffic and a recent inspection of these pavements 
found them in good conditions except where there had "been 
faulty construction. 

Asphaltic concrete Type B. consists of a mixture of 
crushed stone varying in size from that passing a 1" ring 
to that retained on an 8 mesh screen and asphalt, no sand 
or dust being used. This type requires much less asphalt 
in the mixture "but must have a flush coat of about ^. gal. 
per square yard with a coat of screening as described un- 
der Type A. 

What has been said of the quality of stone under Type 
A. applies equally well to Type B. 

The A.C. used is much softer as shown by the follow- 
ing analyses: 







Pioneer 


.bermudez 


Specific Gravity 




.9866 


1.0242 


Melting Point 




1379 F. 


1170 y. 


Flash Point (C.F.) 




430» F. 


360° F. 


Penetration at 0° C. 




59 


19 


■ " 25° C. 




81 


110 


,. " 45° C. 




221 


Too soft 


Loss at 170° C. 5 hrs. 




.33% 


2.92% 


Penetration of residue 


25" 


C. 68 


65 


Solubility in C.S^ 




99.86^ 


97.42% 


" M C C 1 4 




99.80% 


97.88ft 


" " 88 a Be.Naptha 


73.25% 


74.51% 


Fixed Carbon 




9 , 20% 


9 . 83%s 



Coal tars and water gas tars have also been used for 
this type of pavement, particularly in the eastern states 



23 



but they are so susceptible to temperature changes and 

pavements laid with them get so hard and slippery that they 

have not "been very popular. A great deal of experimental 

work has "been done with tar asphalt mixtures. About 12 - 

15 *?o of asphalt is the maximum that can be used safely with 

a tar. If an excess is used it will get "cheesey" and have 

no binding power. When a small percentage of asphalt is 

used the tars are improved because the asphalt makes them 

less susceptible to temperature changes and more stable. 

The following are typical analyses of these materials. 

Coal Tar Water Gas Tar 

Specific Gravity 1.258 1.158 

Float Test ® 50° C. 2 min.30 sec. 23 sec 
Soluble in CS A 70.4% 98.9% 
Organic Matter Insoluble 29.5% 1.1T* 

Ash .17* .05% 

Distillation 



Oils to 110« C. 


.2% 


.03% 


110 - 170 " 


.6% 


.05% 


170 - 270 


10 . 2% 


10.00% 


270 - 315 


n.b% 


19.10% 


Residue 


81.4ft 


69.40<g 



Type C. is a patented pavement, similar to Types A 
and B. It is composed of stone such as is used in type B. 
and sand. This requires a little more A.C. than B. but 
not so much as Type A. The following are the grading 
limits given in the patent:- 



24 



Impalpable powder 1 - 3 % 

" ■ to V 10 - 30f a 

j^_ and larger 50 - 80<7© 

Below is a typical analysis of a pavement of this class. 



Bitumen 






6.0& 


Passing 


200 


mesh 


1.7£ 


n 


80 


n 


2.5% 


it 


40 


•• 


8.8% 


ii 


10 


•• 


35.6*5 


ii 


8 


N 


16.8% 


n 


4 


H 


5.2% 


ii 


2 


II 


18.2% 


ii 


1 


n 


5.2f„ 



It is claimed "by the patentees that the grading used 
gives a minimum of voids producing a maximum density and in- 
herent stability in the pavement which can not be obtained 
by either Type A or B. This however has been disproved by 
the excellent results obtained with the other classes of 
pavements. Their claim that a minimum in percentage of voids 
can only be obtained by such a graded aggregate has also been 
disproved by the writer in some tests made recently in which 
less than 16% of voids were obtained in a mixture of one 
sized crusher run of stone; i.e. passing a 1" ring and re- 
tained on a%^ ring and sand. 

Asphalt pavement is a pavement constructed by what is 
known as the Penetration Method, and is as follows:- Upon 
a crushed stone foundation, similar to a water-bound macadam 
is spread about 3" of clean stone, which will pass a 2" ring 



25 



and "be retained on a ^4- * ring and rolled to an even grade 
when it will be about two inches thick. Over this is spread 
either by pouring cans or other distributors about i-fe gallons 
of bituminous binder to the square yard. A thin coating 
of clean 3 aJ* crushed stone is spread over the surface and 
then thoroughly rolled. The excess of stone is swept off 
and a second pouring of about & gallon to the square yard 
is applied followed by a thin coating of clean '/? " stone 
chips, when the pavement is again well rolled. 

This is perhaps the most uncertain of any of the types 
of bitumunous pavements for there are so many important de- 
tails which are essential that are often neglected. Only 
first class stone, uniform in size should be used in this class 
of construction. The pouring should be done with the great- 
est care and only after thorough rolling and when the stone 
is clean and dry. It is almost impossible to keep from 
getting the bituminous material in streaks when the pouring 
can is used. The Eldus, which is a hand drawn distributor 
has given more uniform results. Many excellent roads have 
been built by this method but it requires a great deal of 
skill and attention to get good results. One great advantage 
is its low first cost which is a great item on country roads 
where traffic is light. 



26 



The bituminous "binders used in asphalt macadam are 
much softer than in sheet asphalt as will be seen from the 
following typical analysis :- 

Pioneer Bermudez Texaco 



Specific Gravity 
Melting Point 
Flash Point (CF) 
Ductility 23° 

■ 0° 

Penetration at 0° 

" " 25 • 

n "450 



.969 
116» F 



4 cm 
2 cm 
95 
183 

Too soft 

Loss © 170° 5 hrs. 2.0% 

Penetration of residue at 25° 0^138 
Solubility in C.8«\ 99.95f c 

M ■ CC1 4 99.96% 

" " ttaptha 88* Beaume76. 25% 
Fixed Carbon 7.74f 

Pariffin Scale 3.14f tf 



1.0427 
109 F 

34.2 cm 
2.0 cm 
37 
132 

Too soft 
4.64% 
33 

96.0455 
95.96f 6 
77. 30^ 
10.84& 
•84f 



.9862 
Liquid 



Too soft 



9.0% 

139 
99.5 % 
99.4 f 
82.2 % 

8.53% 
.22% 



All of the above tests were discussed under sheet asphalt 
except paraffin scale. There has been a great deal of dis- 
cussion as to the value of this test and at present its value 
is very questionable owing to the fact that no standard 
method is in use by which uniform and consistant results can 
be obtained. A large sample divided and sent to half dozen 
different prominent chemists brought as many different re- 
sults, varying from 1 to 5 ^ . In each case the same method 
was supposed to have been used. By slightly varying the 
datails of distillation results varying from 1 jL to 4.5% 
were obtained by the writer, using the same apparatus and 



27 



same sample. 

Bituminous surfaces are used on water-bound macadam 
and gravel roads. These surfaces are formed "by applying a heavy 
residuum oil to the clean dry surface of the road and than 
covering with a thin coating of clean stone chips or coarse 
sand. These surfaces are well suited to medium automobile 
traffic where there is not an excess of horse drawn traffic. 

The first cost of a treatment as described above is very 
low but it has to be repeated from twice a year to every two 
years depending largely on the bituminous material used and 
the traffic conditions. 

Just recently a special material for this class of work 
has been on the market and has been used very successfully on 
water-bound macadam, brick and sheet asphalt pavements. It is 
similar to those used in penetration work but is exceptionally 
adhesive. 

A waterbound macadam treated with '/a gallon per square 
yard two years ago is in excellent shape. An old brick pave- 
ment similarly treated has the appearance of a bituminous 
pavement. A sheet asphalt pavement which was badly cracked 
and had started to disintegrate was repaired by a surface 
treatment and is in good shape. These instances are mentioned 
because so many attempts along this line have failed. The 



28 



following is an analysis of this material :- 

Specific Gravity .97.42 

Melting Point 117° F. 

Penetration at 0° (J. 62 

" 2b* C. 175 

" ■ 45° C. Too soft 

Loss at 170° C. 5 hrs. 2.44% 

Penetration of residue at 25 c C. lu5 

Solubility in CS^ 99.83% 

" M CC1 4 99. 80ft 

w ■ 88<> Be. Naptha 79.03^ 

Fixed Carbon 6.79% 

..any attempts have been made to get a bituminous sur- 
face to adhere to a concrete pavement but have been only 
partially successful. Light tars will adhere for a time but 
as soon as they get cold they become brittle and chip off under 
traffic. Asphalts have been used but traffic seems to a- 
brase the surface of the concrete forming a fine dust which 
allows the bituminous surface to peel off. 

In conclusion it might be said that while the intelli- 
gent use of bituninous materials in road construction is well 
understood by a large number of chemists and engineers there 
is yet room for much research and experimental work which will 
no doubt be done in the near future as the popularity of 
the bituminous pavement is so rapidly increasing.